http://heliquest.ipmc.cnrs.fr.

The Golgi-associated protein ArfGAP1 has an unusual membrane-adsorbing amphipathic alpha-helix: its polar face is weakly charged, containing mainly serine and threonine residues. We show that this feature explains the specificity of ArfGAP1 for curved versus flat lipid membranes. We built an algorithm to identify other potential amphipathic alpha-helices rich in serine and threonine residues in protein databases. Among the identified sequences, we show that three act as membrane curvature sensors. In the golgin GMAP-210, the sensor may serve to trap small vesicles at the end of a long coiled coil. In Osh4p/Kes1p, which transports sterol between membranes, the sensor controls access to the sterol-binding pocket. In the nucleoporin Nup133, the sensor corresponds to an exposed loop of a beta-propeller structure. Ser/Thr-rich amphipathic helices thus define a general motif used by proteins of various functions for sensing membrane curvature.

Two parameters of biological membranes, curvature and lipid composition, direct the recruitment of many peripheral proteins to cellular organelles. Although these traits are often studied independently, it is their combination that generates the unique interfacial properties of cellular membranes. Here, we use a combination of in vivo, in vitro and in silico approaches to provide a comprehensive map of how these parameters modulate membrane adhesive properties. The correlation between the membrane partitioning of model amphipathic helices and the distribution of lipid-packing defects in membranes of different shape and composition explains how macroscopic membrane properties modulate protein recruitment by changing the molecular topography of the membrane interfacial region. Furthermore, our results suggest that the range of conditions that can be obtained in a cellular context is remarkably large because lipid composition and curvature have, under most circumstances, cumulative effects.